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1 SITE REMEDIATION Pedro A. García Encina Department of Chemical Engineering University of Valladolid.

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Presentation on theme: "1 SITE REMEDIATION Pedro A. García Encina Department of Chemical Engineering University of Valladolid."— Presentation transcript:

1 1 SITE REMEDIATION Pedro A. García Encina Department of Chemical Engineering University of Valladolid

2 2 CONTAMINATED SITES In the past much wastes were dumped indiscriminately or disposed of in inadequate facilities. These problems went ignored as did spills of product or leaks from tanks. Theses practices contaminated sites with hazardous substances that pose a threat to human populations.

3 3 HAZARDOUS WASTE - Characteristics Corrosivity -waste that is highly acidic or alkaline, with pH Ignitability -waste that is easily ignited. Reactivity -waste that is capable of sudden, harmful reaction or explosion. Toxicity -waste capable of releasing specified, toxic substances to water in significant concentrations.

4 4 HAZARDOUS WASTE - Major Categories Inorganic Aqueous Waste - liquid waste composed of acids, alkalis or heavy metals in water. Organic Aqueous Waste - mixtures of hazardous organic substances (pesticides, petrochemicals) and water. Oils -liquid waste composed primarily of petroleum derived oils (lubrication oils, cutting fluids). Inorganic Sludges/Solids - sludges, dusts, solids, non- liquid wastes containing hazardous inorganic substances (metal fabricating wastes). Organic Sludges/Solids - tars, sludges, solids and other non- liquid wastes containing organic hazardous substances (contaminated soils).

5 5 Toxicity Characteristics of Hazardous Wastes Acute Toxicity - results in harmful effects shortly after a single exposure, such as cyanide poisoning. Chronic Toxicity - may take up to many years to result in toxic effects, such as cancer or long-term illness.

6 6 HAZARDOUS WASTE TREATMENT Source Reduction Recycling Treatment Disposal


8 8 WASTE MINIMIZATION- PREVENTING TOMORROW´S REMEDIATION PROBLEMS Many of today´s contaminated sites are the result of accepted lawful waste- disposal practices of years ago

9 9 SITE REMEDIATION Source Reduction (?) Recycling(difficult) Treatment Disposal


11 11 SITE CHARACTERIZATION - Definition Site Characterization is defined as the qualitative and quantitative description of the conditions on and beneath the site which are pertinent to hazardous waste management.

12 12 SITE CHARACTERIZATION - Goals The goals of site characterization are to: 1.Determine the extent and magnitude of contamination 2.Identify contaminant transport pathways and receptors 3.Determine risk of exposure

13 13 Zones of Contamination

14 14 groundwater table groundwater flow storage tank floating gasoline gasoline vapors residual gasoline receptors Domestic well Identification of Receptors and Pathways


16 16 METHODS OF SITE CHARACTERIZATION Remote Methods Seismic Survey Soil Resistivity Ground Penetrating Radar Magnetometer Survey Direct Methods Auger Drilling Rotary Drilling Soil Excavation

17 17 REMOTE SUBSURFACE CHARACTERIZATION Seismic Survey GeologicWave MaterialVelocity (m/s) Dry sand Wet sand Clay Water Sandstone Limestone Granite Geophones Seismic wave Soil Rock Source Shock wave propagates faster through rock than soil, depth to rock and rock type can be determined.

18 18 REMOTE SUBSURFACE CHARACTERIZATION Soil Resistivity Resistivity Soil TypeRange (ohm-m) Clays1-150 Alluvium and sand100-1,500 Fractured bedrockLow 1,000s Massive bedrockHigh 1,000s R=soil resistivity(ohm-m) s=electrode spacing (m) V=measured voltage (volts) I=applied current (amperes) Current flow lines s Battery Current Meter Voltage Meter Soil/rock type can be determined by soil resistivity.

19 19 DIRECT SUBSURFACE CHARACTERIZATION Auger Drilling Useful in unconsolidated geologic materials. Sample collection easy, intact samples can be collected with hollow-stem auger. Cannot be used where significant consolidated rock is present. Does not alter subsurface geo- chemistry. Drill Bit Removable Plug Flight Rod inside hollow stem for removing plug

20 20 Rotary Drilling Useful in consolidated geologic materials, can drill through rock. Subsurface samples contaminated with drilling mud. Air-rotary may blow volatile contaminants into surrounding subsurface structures (basements). Mud-rotary alters subsurface chemistry. DIRECT SUBSURFACE CHARACTERIZATION mud pump mud pit

21 21 Drilling through confining layers may allow the spread of contamination from one hydrologic unit to another. DIRECT SUBSURFACE CHARACTERIZATION leaking tank confining layer (clay) uncontaminated water contaminated ground water soil monitoring well

22 22 DIRECT SUBSURFACE CHARACTERIZATION Soil Excavation Useful only in unconsolidated geologic materials to a maximum depth of 10 meters. Large surface disturbance. Excavation not useful for long term groundwater monitoring. No specialized equipment, typically uses backhoe. Subsurface samples can be collected directly. Inexpensive. Good source removal mechanism. Advantages Disadvantages

23 23 SOIL CHARACTERIZATION Soil Contaminant Sampling Performed during drilling or excavation. Collection of samples from several depths within the soil profile. Where volatile compounds are present, sampling should be done in air-tight glass containers. No headspace should be left in the containers. Samples should be chilled for transportation to the laboratory.

24 24 GROUNDWATER CHARACTERIZATION Extent of Contamination: Successive wells should be drilled until the extent of the groundwater contaminant plume is defined.

25 25 AIRBORNE CONTAMINATION Source:Waste pile Release Mechanism:Volatilization Transport Medium:Air Exposure Mechanism:Inhalation or skin contact Exposure Point:May be distant from source, depends on concentration and wind speed

26 26 AIRBORNE CONTAMINATION Measurement Techniques Laboratory Analysis: Samples can be collected in the field in an air-tight bag (Tedlar ) and sampled in the laboratory. Field Analysis: Samples can be analyzed in the field via handheld instrumentation such as a photo-ionization detector for volatile organic compounds or a draw-tube collection device (such as a Drager tube).

27 27 AIRBORNE CONTAMINATION Reducing Airborne Hazards Airborne Hazards Reduction can be accomplished through: Source removal Covering the source (prevents volatilization) Dilution with clean air (if indoors)

28 28 ASSESSING EXPOSURE RISK Definition: Assessment of exposure risk seeks to determine the probability that contamination will migrate to a receptor (human or animal) and be ingested (eaten, inhaled, or absorbed by the skin).


30 30 EXPOSURE PATHWAYS Contaminated groundwater: exposure from drinking or from breathing contaminated vapors liberated during bathing

31 31 EXPOSURE PATHWAYS Inhalation of airborne contaminants: volatilized from the source and carried by wind.

32 32 EXPOSURE PATHWAYS Direct contact with contaminated soil: exposure from skin contact with contaminants in soil.

33 33 EXPOSURE PATHWAYS Indirect contact: exposure to contaminant from crops or animals which have accumulated contamination from soil or groundwater


35 35 DEVELOPMENT OF ALTERNATIVES Identify general response to actions for each objective Characterise media to be remediated Identify potential technologies Screen the potential technologies Assemble the screened technologies into alternatives

36 36 ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost

37 37 ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost Qualitative assessment of how well an alternative meets the remedial action objective over the long term To calculate by means of a complete analysis the residual risk (Risk represented by untreated contaminants or residuals remaining at the site)

38 38 ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost Is only a issue with the alternatives that leave untreated contaminants or treatment residuals at site at the conclusion of the implementation period One tradeoff that require careful consideration at most sites is whether to treat or to contain

39 39 ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability Function of 4. Short term effectiveness 5. Cost History of the demonstrated performance of a technology Ability to construct and operate it given the existing conditions at the particular site Ability to obtain the necessary permits from regulatory agencies

40 40 ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost Deals primarily with the effects on human health an the environment of the remediation itself during its implementation phase Health and environmental risk Worker safety Implementation time

41 41 ALTERNATIVE SELECTION 1. Long term effectiveness 2. Long term reliability 3. Implementability 4. Short term effectiveness 5. Cost The weight given to the cost when evaluating alternatives depend upon the particular guidance of the agency Capital costs (the cost to construct the remedy) Operating and maintenance cost (O & M) (post- construction expenditures)

42 42 TREATMENT ALTERNATIVES On site · In situ · Ex situ (Excavation) Off site (Excavation & Transportation)

43 43 HAZARDOUS WASTE TREATMENT METHODS Physical/Chemical Methods: Mass transfer and chemical transformation processes resulting in the removal or remediation of contamination by abiotic, not combustion means. Biological Methods: Transformation or binding of contaminants by microorganisms, principally bacteria. Waste Stabilization: Containment of wastes such that they pose no further threat to receptors. Combustion Methods: Transformation of organic wastes by burning.

44 44 SOIL VAPOR EXTRACTION Description - soil vapor extraction (SVE) uses a vacuum applied to soil to remove volatile organic compounds (VOCs) from the unsaturated zone. Uses - effective for contaminants with high vapor pressure, such as gasoline compounds, chlorinated solvents. Advantages - low cost, simple design and operation, efficient removal of VOCs from unsaturated zone. Disadvantages - not effective for non-volatile compounds, not effective in low permeability soils or where groundwater is close to the surface, may need to treat off-gas in another process, does not address groundwater contamination.

45 45 SOIL VAPOR EXTRACTION contaminated soil Water Table Contaminated Groundwater air movement through contaminated soil Vapor Extraction Pump

46 46 AIR STRIPPING Description - enhances volatilization of dissolved contaminants from water. Can be used for treatment of either process wastewater or groundwater pumped to the surface. Uses - remove volatile organic compounds (VOCs) from water. Advantages - simple operation, efficient removal of low concentrations of VOCs. Disadvantages - high capital cost, design intensive, may need to treat off-gas in another process.

47 47 Packed Column Air Stripper Intalox saddle Raschig ring Pall ring Berl saddle Tri-pack Water Inlet (contaminated) Air Inlet (clean) Water Outlet (clean) Air Outlet (contaminated) Packing Material Types of Packing Materials

48 48 Packed Column Air Stripper Typical Air-Stripping Column Specifications: Diameter: meters Height: meters Air/Water ratio: Pressure drop: N/m 2 Stripping Column Off-gas Treatment System

49 49 CARBON ADSORPTION Description - carbon adsorption uses granular activated carbon (GAC) to remove organic contaminants from a water or vapor stream. Contaminated air/water is pumped through the GAC unit and contaminants adsorb onto carbon particles by electrostatic forces. Uses - effective for a wide range of organic contaminants. Is commonly used both for process waste treatment and for hazardous waste remediation. Advantages - easy to install, can completely remove many organics, can treat either water or vapor stream. Disadvantages - high operating expense, carbon must be changed periodically, contaminants are not mineralized.

50 50 SOIL WASHING OR FLUSHING Description - Excavated soil is flushed with water or other solvent to leach out contamination. Based on the principles of solid-liquid extraction Uses - remove organic wastes and certain (soluble) inorganic wastes Advantages - simple operation, efficient removal of organic contaminants (VOC, semi VOC and halogenated organics). For metal, it has been successful at extracting organically bound metals (tetraethyl lead) Disadvantages - Longer washing times and soil-handling problems with lower-permeability clays and clay-like soils


52 52 CHEMICAL OXIDATION Description - organic chemicals in extracted groundwater or industrial process wastewater are transformed into less harmful compounds through oxidation by ozone (O 3 ), hydrogen peroxide (H 2 O 2 ), chlorine (Cl 2 ) or ultraviolet radiation (UV). UV is often used in combination with ozone or hydrogen peroxide. Uses - effective for a wide range of organic contaminants such as VOCs, mercaptians, and phenols. Can also be used for some inorganics, such as cyanide. Process is non-specific, oxidant will react with any reducing agent present in the waste, such as naturally occurring organic matter. Advantages - effective, reliable treatment for waste streams which contain a variety of contaminants, often used for drinking water purification. Disadvantages - high operating expense, incomplete oxidation may create chlorinated organic molecules (if Cl 2 is used), generation of oxidizing agent typically cannot vary with fluctuating contaminant concentrations.

53 53 CHEMICAL OXIDATION Reactor Configuration H 2 O 2 Storage Influent flowm eter Effluent Control System Power System Reaction Chamber UV Lamps

54 54 CHEMICAL OXIDATION - Results Fraction TCE Remaining Initial TCE =58 mg/L

55 55 CHEMICAL OXIDATION - Results Halogenated aliphatic destruction by H 2 O 2 and UV at 20 o C.

56 56 CHEMICAL OXIDATION - Design Considerations Thermodynamics: Free energy available from reactions OxidantFree Energy (E, volts) O H 2 O Cl Kinetics: Reaction must proceed to necessary completion within the residence time in the reactor vessel. Combination of UV with ozone or hydrogen peroxide increases reaction kinetics. Design Steps: 1) Will oxidation reaction proceed with contaminants present? 2) What is the contact time necessary between the oxidant and the contaminants present?

57 57 SUPERCRITICAL FLUID EXTRACTION Description - contaminated liquid or solid is placed in a reactor vessel with the extraction fluid, which is heated and pressurised to the critical point (see chart). In treatment of hazardous wastes, fluids most commonly used are water and CO 2, some organic solvents may also be used. Uses - supercritical fluid extraction can be used to treat contaminated soils, sediments, sludges, solids or liquids. Advantages - effective treatment for process wastes or extracted soil or groundwater which is either highly contaminated with organic compounds or with very recalcitrant (hard to treat) organics Disadvantages - expensive, solids must be reduced in size to 100 um to pass through high pressure pumps.

58 58 SUPERCRITICAL FLUID EXTRACTION Reactor Configuration Schematic diagram of reactor for the extraction of organic compounds from water, CO 2 is the extraction fluid.

59 59 SUPERCRITICAL FLUID EXTRACTION Solvent Selection Criteria Cost - water, CO 2 are least expensive Recoverability - solvent must be recoverable for process to be economical Hazard in use - SFE involves high temperatures and pressures which reactor vessels must be built to withstand Critical temperature and pressure - the higher the critical T and P of the solvent, the greater the operating expense Distribution coefficient - determines the solvent/ contaminant ratio which can be used.

60 60 MEMBRANE PROCESSES Electrodialysis - separation of ionic species from water by direct-current electric field. Useful for removal of charged ions and metals from water. Reverse Osmosis - solvent is forced through a semi- permeable membrane by the application of pressures in excess of the osmotic pressure. Useful for removal of metals and some organics. Ultrafiltration - separates dissolved contaminants on the basis of molecular size. Lower limit for molecular weight is approximately 500.

61 61 BIOLOGICAL PROCESSES Description - biodegradation uses micro-organisms (bacteria) to remove organic contaminants from vapors, liquids or solids. Most organic contaminants are utilized by bacteria as both a carbon and energy source. Uses - biological processes are effective on both process waste streams and remediation of soil and groundwater. Biodegradation systems for soil and groundwater can by designed either in-situ (in place) or ex-situ (removed from the ground). Advantages - low cost, low site disturbance, effective for many organic contaminants. Disadvantages - long clean-up times, not effective for inorganic contaminants, specialized conditions necessary for chlorinated solvent degradation.

62 62 BIOLOGICAL PROCESSES Necessary Constituents: microorganisms capable of degrading contaminants contaminants in aqueous (water) phase available electron acceptor present Aerobic Degradation: takes place in the presence of molecular oxygen (O 2 ), the most energetically favorable electron acceptor. Anaerobic Degradation: when O 2 is not available, other compounds can act as electron acceptors for biodegradation processes, such as NO 3, Fe +3, Mn +4, SO 4, and CO 2.

63 63 Energy Available from Electron Acceptor Processes Electron Acceptor G o (kJ/ mol mineralized) O 2 NO 3 Fe +3 SO CO Toluene Benzene -, Mn +4 ~ ~

64 64 BIOLOGICAL PROCESSES - Remediation of soil and groundwater In-situ biodegradation: Natural attenuation Engineered systems Ex-situ biodegradation: Pump and treat systems for groundwater Landfarming systems for soil treatment

65 In-Situ Biodegradation - Natural Attenuation

66 66 Typical Contaminant / Electron Acceptor Concentrations with Distance Natural Attenuation of Contaminants

67 67 Aerobic Respiration 10% Denitrification 14% Iron (III) Reduction 8% Sulfate Reduction 29% Methanogenesis 39% Relative Importance of Electron Acceptor Processes at 25 Air Force Sites Source: Wiedemeier et al., 1995

68 68 Stoichiometric Conversion Example: Iron Reduction BTEX + 36Fe H 2 O 36Fe CO 2 + 7H 2 O Assume 20 mg/l Fe +2 observed in aquifer Calculate BTEX consumed per unit volume: (20 mg/l Fe +2 produced ) 1 mmol Fe mg Fe +2 ( ) 1 mmol BTEX 36 mmol Fe +2 ( ) 92 mg BTEX 1 mmol BTEX ( ) = 0.9 mg/l BTEX consumed in aquifer Calculate groundwater flux and total BTEX consumed: Assume: V gw = 1 ft/day Plume width = 100 Plume height = 10 Flux = vwh = 1000 ft 3 /d = 7500 gal/d = 28x10 3 l/d BTEX consumed = (28x10 3 l/d) (0.9 mg/l) = 25 g BTEX/day

69 69 In-Situ Biodegradation - Engineered Systems water/nutrient supply tank air compressor injection well water table contaminated soil air sparger confining layer pump Groundwater treatment unit Air-sparging/nutrient addition system

70 70 In-Situ Biodegradation - Engineered Systems Infiltration gallery, recirculating system

71 71 In-Situ Biodegradation - Engineered Systems Combination air injection/extraction system water table

72 72 In-Situ Biodegradation - Engineered Systems Air injection bioventing

73 73 Ex-Situ Biodegradation - Pump and treat Water Table Liquid Hydrocarbon Contaminant Skimmer Pump Vacuum Air removal Oil/water Separator Vacuum Pump Liquid phase Bioreactor

74 74 Ex-Situ Biodegradation - Biofiltration Contaminated Soil Vapor Extraction Well Blower Moisture Addition Biofilter Biofilter is colonized with bacteria capable of degrading contaminants. Media can be soil, peat, compost, or manufactured packing material.

75 75 Ex-Situ Biodegradation - Biopiles Gas Monitoring Probes Air Intakes Irrigation Piping Weights Aeration Pipes Wood Chips Tarp Crushed Stone Soil Curb Leachate Pipe Impermeable Base Aeration Pipe Contaminated Soil

76 76 Ex-Situ Biodegradation - Landfarming Procedures: Excavated soils are spread onto the ground surface to a depth of less than 0.5 meters. Underlying soils should be low permeability, or a clay liner or impermeable membrane should be used to prevent contaminant migration to groundwater. Landfarmed soils should be tilled every 2-3 months and kept moist.

77 77 WASTE STABILIZATION AND CONTAINMENT Procedure: Excavated soils or process wastes are secured such that contaminant migration will not occur (containment), or are mixed with binding agents that solidify the waste and prevent leaching or release of the contaminants (stabilization). Processes: Encapsulation Sorption processes Polymer stabilization In-situ vitrification

78 78

79 79

80 80 COMBUSTION METHODS Description: waste combustion can take place in hazardous waste incinerators, cement kilns, or industrial boilers. Most significant design parameter is the heat value of the waste. Many concentrated organic wastes will support combustion without supplemental fuel. Applicable wastes: all organic wastes can be mineralized using combustion methods. Metals are oxidized in the combustion process and are either vented in gaseous form or are concentrated in ash. Metals prone to gaseous emission are arsenic, antimony, cadmium, and mercury. Procedure: Wastes are graded for suitability for combustion. Waste analysis also indicates the proper fuel/air mixture for complete combustion.

81 81

82 82 CONTAINMENT Frecuently it is necessary to minimize the rate of off site contaminant migration employing containments technologies to minimize risk to public health and environment. Containment technologies may be associated with other technologies to implement a long-term clean- up strategy for the site

83 83 CONTAINMENT Active system components require considerable effort and on-going energy in put to operate (For example pumping wells) Pasive system components work without much attention, except maintenance (such a cover)



86 86

87 87 SELECTION OF REMEDIAL ALTERNATIVES 1. Data Needs A.Site Characterization B.Regulatory Disposition C.Risk Assessment 2. Establishment of Site Objectives A.Clean-up Level Necessary B.Long-term Liability C.Costs 3. Development and Analysis of Alternatives A.Development of Possible Alternatives B.Analysis of Alternatives for Effectiveness 4. Remedial Option Selection, Implementation, and Monitoring A.Remedial Option Selection B.Implementation C.Long term Site Monitoring

88 88 SELECTION OF REMEDIAL ALTERNATIVES Data Needs: Understand extent and magnitude of contamination. A thorough site characterization is necessary. Chemical fate and transport must be understood. Determine risk to potential receptors. This is necessary to correctly focus efforts where they are most needed. Typical exposure pathways include groundwater wells and airborne contaminants. Determine what limits or requirements are placed on the clean up by government regulations. It is important to insure that all participants understand and agree on the goal of the remedial effort.

89 89 SELECTION OF REMEDIAL ALTERNATIVES Establishment of Site Objectives: Establishment or negotiation of acceptable clean-up goals is necessary prior to selection of a remedial process. The extent of long-term liability for the site should be considered. Costs of each remedial option must be considered along with the financial means of the financially responsible party. Options for cost assistance should be considered at this stage (national and international).

90 90 SELECTION OF REMEDIAL ALTERNATIVES Development and Analysis of Alternatives: A list of potential remedial alternatives is compiled for further study based on their feasibility to clean up the site. Criteria for selection of a remedial alternative are effectiveness, reliability, cost, time to implementation, and time to clean up. Before a remedial solution is chosen, a detailed plan of implementation should be formulated to insure that the technique is capable of remediating the site to the goals prescribed.

91 91 SELECTION OF REMEDIAL ALTERNATIVES Remedial Option Implementation and Monitoring: After a remedial option is selected, construction contracts and engineering designs must be completed. Can be done by employee engineers or contractor engineers (must be familiar with technology chosen). Long term site monitoring should continue to insure that the solution is working, and that further contaminant migration does not occur. Monitoring should include all applicable media (groundwater, soil vapor, and air).



94 94 LEY 10/98 DE RESIDUOS CONTAMINATED SITES · Depends of Comunidades Autónomas · List of contaminated places (priority to clean-up) · Need to clean-up the site · The responsible of the contamination · The owner of the site





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